初三数学题~`~~```````

已知X^2-2X=2,将下式先化简，在求值：
（X-1)^2+(X+3)(X-3)+(X-3)(X-1)
=x^2-2x+1+x^2-9+X^2-4X+3
=3X^2+-6X-5
=3(X^2-2X)-5
=3*2-5
=6-5
=1

（X-1)^2+(X+3)(X-3)+(X-3)(X-1)
=x^2-2x+1+x^2-9+x^2-4x+3
=3x^2-6x-6
=3(x^2-2x)-6
原式=6-6
=0

1

（X-1)^2+(X+3)(X-3)+(X-3)(X-1)
=X^2-2x+1+x^2-9+x^2-4x+3
=3x^2-6x-5
=3(x^2-2x)-5

代入X^2-2X=2
=3*2-5
=1

很方便呀
将（X-1)^2+(X+3)(X-3)+(X-3)(X-1) 全部拆开来
得到
X方-2X+1+X方-9+X方-4X+3
= 3X方-6X-5
= 3(X方-2X)-5

然后已知X方-2X=2
带入就可以了
=1

X-1)^2+(X+3)(X-3)+(X-3)(X-1)
=x^2-2x+1+x^2-9+x^24x+3
=3x^2-6x-5
套公式